Filters for use with magnifying binoculars have been proposed heretofore and examples of such proposals are disclosed in U.S. Pat. Nos. 2,383,186; 2,408,772; and 3,528,724. The filters disclosed in these patents are polarized filters and are mounted externally of the binocular case. The external mounting of the filters is necessary so as to enable the filters to be used or not to be used, as desired. The external mounting of filters, however, subjects them to excessive wear and damage.
Polarized filters are useful for many purposes, but other filters are equally useful for different purposes. In those instances in which polarized filters are provided for binoculars, they either must be used at all times or dismounted from the binocular case. If another filter is to be used, it must be substituted for the polarized filters, thereby resulting in a tedius and time consuming adjustment.